SizeKit guides
Plain-English explanations that go with SizeKit’s tools: how the calculations work, what the results mean and where they can mislead.
Calculators, measurements and everyday maths
- How to calculate percentagesThe three questions behind almost every percentage problem, with worked examples and shortcuts you can do in your head.
- Percentage change explainedHow to calculate an increase or decrease, why +50% then −50% does not get you back, and percent versus percentage points.
- How discounts and sale prices workWorking out sale prices, finding the real discount from two prices, and why stacked discounts do not simply add up.
- How BMI is calculated and what it can and cannot tell youThe formula, the adult categories, and the honest limits of a number built from only height and weight.
- How age is calculated in years, months and daysWhy counting birthdays is simple but counting months is not, and how leap days and end-of-month dates are handled.
- Unit conversion basicsHow conversion factors work, which ones are exact, and the mistakes that cause most wrong answers.
- How to measure your height and weight accuratelyPractical steps for consistent measurements at home, and how to convert them between metric and imperial.
Photo size and upload requirements
- How to compress an image to 100 KBA step-by-step walkthrough, a tested example and what to do when your photo cannot fit.
- KB versus pixels: why changing one is not enoughRead a form’s size rules correctly, preserve proportions and avoid stretching.
- JPG or WebP for online forms?Choose an accepted output format, understand transparent backgrounds and avoid extension-only conversions.
US visa, passport and Diversity Visa photos
- US visa photo size: 600 × 600 pixels and 240 KB explainedThe State Department’s technical rules for visa photos, the 20:1 compression limit explained, and how to prepare a compliant file.
- US online passport renewal photo: file size and format rulesFile size and format rules for online renewal, how they differ from visa photos, and why you usually should not resize first.
- Diversity Visa (DV) lottery photo requirements: size, format and file sizePhoto size, format and family requirements for the Diversity Visa lottery, with the mistakes that disqualify entries.
- How to compress a photo to 240 KB without changing its pixel sizeKeep 600 × 600 pixels and get under 240 KB, with the arithmetic for how much compression different sizes need.
- Why a US government photo upload gets rejected (and how to fix it)Match the rejection symptom to the cause: wrong rule set, file problems you can fix, and photo problems that need a retake.
- “Head size or position may be incorrect” on a US visa photo: how to fix itWhat the 50–69% head rule and the eye-line band mean in pixels, and how to re-crop the original to pass.
- “Illumination appears to be poor” on a US photo upload: how to fix itA lighting error, not a file error: the likely causes, a fix table and a retake checklist.
- DS-160 photo upload error: what to do when you cannot continueTell a file problem you can fix from a website problem you cannot, and the steps applicants report trying.
Pakistan forms, passport photos and signatures
- Pakistan passport photo requirements for the online applicationWhat the official e-Services page says about the online photo, and why cropping or editing it is the wrong move.
- Passport photo size in mm, inches and pixels: how to convertConvert 35 × 45 mm and 2 × 2 inch photo sizes into pixels at 300 and 600 ppi, with worked examples.
- How to prepare a signature image for online formsPhotograph, crop and resize a signature without stretching it, and fit a small KB limit.
- How to reduce a photo to 50 KB or 20 KB for online formsWhy tiny limits are hard, a table of how much compression each size needs, and how to get under 50 or 20 KB.
How these guides are written
Each guide explains a real question behind one of the tools, uses worked examples you can check by hand, and says where a result should not be trusted blindly. They are written by the site owner and updated when a tool or its rules change. If you spot a mistake, please tell us.
Ready to calculate? Visit the calculators and converters or open the photo resizer.